The invention relates to a method of arranging twine around a bale of, for instance, straw or hay formed by pressing in a baling machine, including tying the twine off by knotting it.
The invention relates furthermore to apparatus for carrying out the method, made up of knotting apparatus which can be combined with a baling machine.
A method and an apparatus have been commonly known, particularly in agriculture, since the thirties, in which the bale is formed in a bale chamber against a piece of twine extending through the chamber and, after completion of the bale, a needle performs a reciprocating movement across the back of the bale and through the press plunger so as to surround the bale with twine, after which the twine, while the pressure is still maintained, is tied off. The work is done with a piece of twine coming from one single bobbin. After enclosing the bale, a knot is made by means of a knotting apparatus which comprises a so-called retainer as an essential part. The use of retainers entails a number of disadvantages and sensitivities. In the course of time, various improvements in regard to details have been proposed, but in principle the way in which the retainers work has not been changed in comparison with the original design. Since in these known retainers the twine to be knotted is clamped between the plates, a number of sensitivities arise, most of which are conductive to the untimely slipping of the twine out of the retainer. In the first place, it is evident that there exists a sensitivity to the thickness of the twine used but, therefore in the second place, also to variations in the thickness such as may occur particularly with flax twine. However, the thickness alone is not decisive, for the kind of twine is also of influence on the grip the retainer has on the twine. Thus twine of natural fibres has a better internal cohesion than twine made of plastics material; there are, for instance, several kinds of polypropylene twine in the market, on the one hand in the shape of fibres and, on the other hand, in the shape of twisted foil, but either kind has the disadvantage that the elements of the twine, particularly in the interior of the twine, can easily slip along each other, as a result of which the retainer may lose its grip on the twine. Furthermore, the retainer is sensitive to pollution bur moreover to wear of the various parts of the retainer itself. Further, there occurs, of course, wear in the parts of the retainer rotating with respect to each other.
Given these sensitivities and problems, work could nevertheless be done reasonably well in actual practice provided measures were taken to ensure that the tension in the twine remained limited. This entailed at least a limitation in the compressive force. As an indication may be mentioned that up to now, with optimum adjustment of the retainer, it was not possible in baling presses to exceed 130 kg/m.sup.3 for hay.
Advantages may be achieved by bringing heavier pressures to bear. On the one hand, there is, of course, the aspect of the storage capacity for a certain quantity by weight, but on the other hand there is the very important factor of the cost of transport. The said value of 130 kg/m.sup.3 usually implies that a lorry will have a maximum load by volume whereas its load by weight at that moment is in the vicinity of half the admissible value only. In the ideal case it would be possible to convey twice that quantity of material provided it could be compressed to one half.
Apart from these problems and sensitivities of the retainer, raising the pressure meets with still another problem. The twine is displaced between the bale which has just been tied off and the bale to be newly formed. Each stroke of the pressing plunger implies a tug to the twine which is kept between the flakes (successively pressed portions) and the retainer. When the compression is increased these tugs become more intense and the likelihood of the twine being stresses to break or of its being drawn out of the retainer increases. The increase in this likelihood is more than proportional above a certain limit.
One of the solutions is binding with wire, generally iron wire, whether or not galvanized. This has a greater tensile strength than twine. The application of wire has been known as such at least as long as binding with twine. However, there are again some specific disadvantages connected therewith which have meant that, in some countries anyhow, the use of strapping wire has been abandoned in the domain of agriculture. One of the disadvantages is the formation of rust, but the most important is the risk of pieces of iron wire getting between the fodder which, as is known, may cause the cattle to die as a consequence of gastric or intestinal perforations. Apart from this, there is still a limit to the compression rate when iron wire is used. The extreme ends of the wire are twisted and the twist will loosen when the bale compression becomes too high.
The principle object of the invention therefore is to provide a method and apparatus with which it is possible, while making use of twine (whether of natural or of plastics fibres) to raise the admissible pressure considerably.
Another important object to provide this in such manner that during the process of bale forming and surrounding it with twine and tying it off there is no tension in the twine related to the pressure extended on the bale which is being formed.
A further object is to eliminate the need for the conventional retainer.
A still further object is to reduce as far as possible the time required for tying off the bale.